1. Field of the Invention
The present invention relates to a polylactic acid composition, and more particularly relates to a polylactic acid composition suitable for a material of an automobile part such as a bumper.
2. Related Background Art
Polylactic acid has a degradable property by activities of microorganisms or enzymes, so-called biodegradability, and is decomposed to lactic acid, carbon dioxide and water, which are harmless to humans. Thus, polylactic acid has drawn attention as an alternative to a medical material or a general-purpose resin. Moreover, as to a polylactic acid composition containing such polylactic acid, research and development have been conducted to allow the composition to have properties such as drawability and flexibility.
For example, Japanese Unexamined Patent Application Publication No. 2003-313401 (JP 2003-313401 A: Document 1) discloses an aliphatic polyester composition containing aliphatic polyester and an alcohol lignin derivative or a cinnamate ester derivative, which is mixed as a plasticizer in the aliphatic polyester by 10 wt % or less. However, a polylactic acid composition containing an alcohol lignin derivative or a cinnamate ester derivative by 10 wt % or less, that is a type of the aliphatic polyester composition described in Document 1, has not yet been sufficient in terms of drawability.
Moreover, there has been disclosed a polylactic acid composition containing a large amount of ester-based plasticizer in polylactic acid. For example, Japanese Unexamined Patent Application Publication No. 2000-302956 (JP 2000-302956 A: Document 2) discloses an aliphatic polyester composition including 100 part by weight of aliphatic polyester and 10 to 60 parts by weight of at least one compound selected from compounds (B) which are reaction products of 1 to 10 glycerol molecules and carboxylic acid having carbon numbers of 6 to 18. Moreover, Japanese Unexamined Patent Application Publication No. Hei 11 (1999)-35808 (JP 11-35808 A: Document 3) discloses a lactic acid based polymer composition including an ether ester plasticizer of weight-average molecular weight 150 to 30000. Furthermore, Japanese Unexamined Patent Application Publication No.2003-231798 (JP 2003-231798A: Document 4) discloses a lactic acid based resin composition which consists mainly of 67 to 96 Wt % of a lactic acid based resin and 4 to 33 Wt % of a plasticizer of which boiling point is 220° C. or higher under a normal pressure or of which boiling point is 170° C. or higher at 5 to 10 Torr. However, although such polylactic acid compositions described in Documents 2 to 4 show drawability and flexibility, the compositions have not yet been sufficient in terms of a characteristic of retarded elastic recovery. Specifically, the retarded elastic recovery means a behavior of gradual recovering to an approximately original shape without instantaneous drastic deformation recovery, in the case where stress is released after large deformation which deviates from a linear viscoelastic behavior.